Substituted tolylesters of PGF{HD 2{B {60

ABSTRACT

Substituted phenyl and naphthyl and 9-oxofluoren-4-yl esters of PGF2 Alpha , 15-alkyl-PGF2 Alpha , and 15(R)-15-alkyl-PGF2 Alpha , and their racemic forms, and processes for producing them are disclosed. The products are useful for the same pharmacological and medical purposes as PGF2 Alpha , 15-alkyl-PGF2 Alpha , and 15(R)-15-alkyl-PGF2 Alpha , and are also useful as a means for obtaining highly purified PGF2 Alpha , 15-alkyl-PGF2 Alpha , and 15(R)-15-alkyl-PGF2 Alpha products.

United States Patent 1 1 3,929,862

Morozowich Dec. 30, 1975 SUBSTITUTED TOLYLESTERS 0F PGF a 807,046 5 1974 Belgium 260/468 [75] Inventor: Walter Momzowich, Kalamazoo 807,047 5 1974 Belgium 260/468 Primary Examiner-R obert Gerstl Asslgneel The pj p y, Kalamazoo. Attorney, Agent, or Firm-Mo'rris L. Nielsen; Bruce Mich. Stein 22] Filed: Sept. 30, 1974 Appl. No; 510,233

Related U.S. Application Data FOREIGN PATENTS OR APPLICATIONS 5/1974 Belgium 260/468 57 ABSTRACT Substituted phenyl and naphthyl and 9-oxofluoren-4-yl esters of PGF a, IS-aIkyI-PGF a, and l5(R)-l5-alkyl- PGF a, and their racemic forms, and processes for producing them are disclosed. The products are useful for the same pharmacological and medical purposes as PGF a, l5-alkyl-PGF a, and l5(R)-15-alkyl-PGF a, and are also useful as a means for obtaining highly purified PGF a, IS-aIkyI-PGF a, and l5(R)-l5-alkyl- PGF a products 8 Claims, No Drawings SUBSTITUTED TOLYLESTERS, OFPGFz This is a division of application Ser. No. 431,758, filed Jan. 8, 1974.

BACKGROUND OF THE INVENTION This invention relates to novel ester derivatives of prostaglandin F (hereinafter identified as PGF a), l5-alkyl-PGF a, (R)-15-alkyl-PGF 1,and their racemic forms, and to processes for producing them.

PGF a is represented by the formula:

A systematic name for PGF a is 7- 3a,'5a-dihydroxy- 2B-[(3S )-3-hydroxy'-trans- 1 -octenyl]- 1 a-cyclopentyl cis-S-heptenoic acid. PGF a is known to be useful for a variety of pharmacological and medical purposes, for example labor induction and abortion in pregnant animals, including humans, menstrual regulation in both pregnant and non-pregnant animals, including-humans, and reduction and control of gastric secretion. See Bergstrom et al., Pharmacol. Rev. 20, 1 (1968) and references cited therein. As toracemic PGF a, see for example E. S. Corey et al., J. Am. Chem. Soc., 91, 5675 (1969).

The 15-alkyl-PGF a analog and its 15(R) epimer are represented by the formula:

wherein Y is following the usual convention wherein broken line attachment of hydroxy to the side chain at carbon 15 indicates the natural or S" configuration and solid line attachment of hydroxy indicates the epi or R configuration. See for example Nugteren et al., Nature 212, 38 (1966) and Cahn, J. Chem. Ed. 41, 116 1964). The l5-alkyland 15(R)-15-alkyl-PGF a analogs in their optically active and racemic forms are known. See for example U.S. Pat. No. 3,728,382. These analogs are also useful for the above-described pharmacological purposes. I Y

Esters of the above compounds are known, wherein the hydrogen atom of the carboxyl group is replaced by a hydrocarbyl or substituted hydrocarbyl group.

Among these are the methyl ester of PGF a (B. Sam- SUMMARY OF THE INVENTION wherein Z is the substituted phenyl or naphthyl group or fluorenone as defined immediatelybelow, and Y is i.e. esters of PGF a, 15-methyl-PGF a, 15(R)'-15- methyl-PGF a, 15-ethyl-PGF a and l5(R)-l5-ethyl- PGF a; and also the racemic compounds represented by each respective formula and the mirror image thereof; Z being represented O 11 A NH-C-CH3 ll B Q 4 o 1 i II I C if r Q Q NH- C-NHQ E o .4 ll v. @NH-C-NHQ. U r

N H c c11 SO NH For example, PGF a, p-acetamidophenyl ester, is represented by formula III wherein Y is H OH and Z is A, i.e.

and is conveniently identified herein as the PGF a ester of formula III-A. Racemic compounds are designated by the prefix racemic or dl; when that prefix is absent, the intent is to designate an optically active compound. Racemic l5-methyl-PGF a, p-benzamidophenyl ester, corresponds to formula III wherein Y is and Z is B, i.e.

including of course not only the optically active isomer represented by formula III but also its mirror image.

The novel formula-III compounds and corresponding racemic compounds of this invention are each useful for the same purposes as described above for PGF a and are used for those purposes in the same manner known in the art, including oral, sublingual, buccal, rectal, intravaginal, intrauterine, or topical administration.

For many applications these novel prostaglandin esters which I have obtained from certain specified phenols, naphthols, and hydroxyfluorenone have advantages over the corresponding known prostaglandin compounds. In oral adminstration these esters have shown surprisingly greater efficacy than the corresponding free acids or lower alkyl esters, whether because of longer duration of biological activity or because of improved lipophilicity and absorption is not certain. These esters offer a further advantage in that g? they have low solubility in water and the body fluids and are therefore retained longer at the site of adminstration. 5 o

A particularly outstanding advantage of many of these substituted phenyl and naphthyl and hydroxy- Q 2 fluorenone esters is that they are obtained in free-flowing crystalline form, generally of moderately high melt 7 ing point, in the range 90-l80 C. This form is especially desirable for ease of handling, administering, and Q purifying.

These crystalline esters also provide a means of purifying PGF a, IS-methyI-PGF a, l5(R)-l5-methyl- I o Pom, l5-ethyl-PGF a, or l5(R)-l5-cthyl-P(1F a, H which are first converted to one of these esters, recrys- Q 'Q I SH tallized until pure, and then recovered as the free acid. 2 I One method of recovering the free acid is by enzymatic o l hydrolysis of the ester, for example with a lipase. See 20 @l German Pat. No. 2,242,792, Derwent Farmdoc No. 3

To obtain the optimum combination of stability, duration of biological activity, lipophilieity, solubility, and j erystallinity, certain compounds within the'seope of formula III are preferred. 25

One preference is that 7. is limited to either o NJJ ll @uwc-ma; 4s

0 I I H ii-c-im uwom+ U o u 0 @(H iH-f-NH, g

war-0 M A I Y I n Another preference is that 'l. is further limited to ()5 wherein R is Another preference is that Z is limited to r mw.

0 ll @CHIN-NH-C-NHT Another preference is that Z is limited to wherein Ris 3 wherein R is Especially preferred are those compounds which are in free-flowing crystalline form, including:

ester of ester of The substituted phenyl and naphthyl and 9-oxofluoren-4yl esters of PGF a, l5-alkyl-PGF a, and l5(R)- l 5- alkyl-PGF a encompassed by formula III wherien Z is defined by ester groups A through Z are produced by the reactions and procedures described and exemplifled hereinafter. For convenience, "the above prostaglandin or prostaglandin analog is referred to as the PG compound. The term phenol is used in a generic sense, for the hydroxy compounds, including phenols, naphthols, and hydroxyfluorenone.

Various methods are available for preparing these esters, differing as to yield and purity of product. Thus, by one method. the PG compound is converted to a tertiary amine salt, reacted with pivaloyl halide to give the mixed acid anhydride and then reacted with the phenol Altcrnately, instead of pivaloyl halide, an alkyl or phenylsulfonyl halide is used, such as p-toluenesulfonyl chloride. See for example Belgian Pat. Nos. 775,]06 and 776,294, Derwent Farmdoc Nos. 33705T and 3901 IT.

Still another method is by the use of the coupling reagent, dicyclohexylearbodiimide. See Fieser et al., Reagents for Organic Synthesis", pp. 231-236, John Wiley and Sons. Inc, New York (i967). The PG compound is contacted with one to ten molar equivalents of for the optically active PG compounds, Y having the same definition as above.

The anhydride is formed readily at temperatures in the range 40 to +60 C., preferably at l to +10 C. so that the rate is reasonably fast and yet side reactions are minimized. The isobutylchloroformate reagent is preferably used in excess, for example 1.2 molar equivalents up to 4.0 per mole of the PG compound. The reaction is preferably clone in a solvent and for this purpose acetone is preferred, although other relatively non-polar solvents are used such as acetonitrile, dichloromethane, and chloroform. The reaction is run in the presence of a tertiary amine, for example triethylamine, and the co-formed amine hydrochloride usually crystallizes out, but need not be removed for the next step.

The anhydride is usually not isolated but is reacted directly in solution with the phenol, preferably in the presence of a tertiary amine such as pyridine.

The phenol is preferably used in equivalent amounts or in excess to insure that all of the mixed anhydride is converted to ester. Excess phenol is separated from the product by methods described herein or known in the art, for example by crystallization. The tertiary amine is not only a basic catalyst for the esterification but also a convenient solvent. Other examples of tertiary amines useful for this purpose include N-methylmorpholine, triethylamine, diisopropylethylamine, and dimethylaniline. Although they may be used, Z-methylpyridine and quinoline result in a slow reaction. A highly hindered amine such as 2,6-dimethyllutidine is not useful because of the slowness of the reaction.

The reaction with the anhydride proceeds smoothly at room temperature (about 20 to 30 C.) and can be followed in the conventional manner with thin layer chromatography (TLC), usually being found complete within 1-4 hours.

The reaction mixture is worked up to yield the ester following methods known in the art, and the product is purified, for example by silica gel chromatography.

Solid esters are converted to a free-flowing crystalline form on crystallization from a variety of solvents, including ethyl acetate, tetrahydrofuran, methanol, and acetone. by cooling or evaporating a saturated solution of the ester in the solvent or by adding a miscible nonsolvent such as diethyl ether, hexane, or water. The crystals are then collected by conventional techniques, e.g. filtration or centrifugation. washed with a small amount of solvent, and dried under reduced pressure. They may also be dried in a current of warm nitrogen or argon, or by warming to about 75C. Although the crystals are normally pure enough for many applica- 10 tions, they may be recrystallized by the same general techniques to achieve improved purity after each recrystallization.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention can be more fully understood by the following examples.

All temperatures are in degrees centigrade.

Silica gel chromatography, as used herein, is understood to include chromatography on a column packed with silica gel, elution, collection of fractions, and combination of those fractions shown by thin layer chromatography (TLC) to contain the desired product free of starting material and impurities.

TLC", herein, refers to thin layer chromatography.

PREPARATION l p-Benzamidophenol A solution of p-hydroxyaniline (20 g.) is 200 ml. of pyridine is treated with benzoic anhydride (20 g.). After 4 hr. at about 25 C., the mixture is concentrated under reduced pressure and the residue is taken upv in 200 ml. of hot methanol and reprecipitated with 300 ml. of water. The product is recrystallized from hot acetonitrile as white crystals, 8.5 g., m.p. 2l8.02l 3.5 C.

PREPARATION 2 p-(p-Acetamidobenzamido )phenol A solution of p-aeetamidobenzoie acid (12.5 g.) in 250 ml. of tetrahydrofuran is treated with triethylamine (l 1.1 ml.). The mixture is then treated with isobutylchloroformate (l0.4 ml.) and, after 5 min. at about 25C., with p-aminophenol (l3.3 g.) in ml. of dry pyridine. After 40 min. the crude product is obtained by addition of 2 liters of water. The product is recrystallized from 500 ml. of hot methanol by dilution with 300 ml. of water as white crystals, 5.9 g., m.p. 275.0-277.0 c.

EXAMPLE 1 p-Acetamidophenyl Ester of PGF a (Formula III-A).

A solution of PGF a (0.535 g.) and triethylamine (0.254 ml.) in 20 ml. of acetone is treated at -l0 C. with isobutylchloroformate (0.238 ml.) whereupon triethylamine hydrochloride is precipitated. After 5 min. the mixture is treated with p-acetamidophenol (0.342 g.) in 5 ml. of pyridine for 3 hr. at about 25C. The solvent is removed under reduced pressure and the residue taken up in acetonitrile and again concentrated. The crude residue is subjected to silica gel chromatography, eluting with ethyl acetate-methanol (-10). The residue obtained by concentration of selected fractions, a solid on chilling, is the title compound 0.285 g., having R, 0.6 (TLC on silica gel in ethyl acetate-methanol 90:l0). It is recrystallized from ethyl acetate-hexane as white free-flowing crystals, m.p. ll4-ll5.8 C.

EXAMPLE 2 p-Benzamidophenyl Ester of PGF a (Formula III-B) Following the procedure of Example 1 but using 0.535 g. of PGF a, 0.254 ml. of triethylamine, 0.238 ml. of isobutylchloroformate, and 0.481 g. of p-benzamidophenol (Preparation 1), there is obtained a crude residue. This residue is subjected to silica gel chromatography. eluting with ethyl acetate followed by ethyl acetate-methanol (:5). The residue obtained by concentration of selected fractions, 0.220 g., is crystallized from ethyl acetate-methanol (100:5) diluted with hexane as the title compound, white free-flowing crystals, m.p. 139.8l43.8 C., having R, 0.8 (TLC on silica gel in ethyl acetate-methanol (95:5)).

EXAMPLE 3 p-Ureidophenyl Ester of PGF a (Formula lll-E) Following the procedure of Example 1 but using 0.738 g. of PGF a, 0.306 ml. of triethylamine, 0.288 ml. of isobutylehloroformate, and 0.330 g. of p-hydroxyphenylurea, there is obtained a crude residue. This residue is subjected to silica gel chromatography, eluting with ethyl acetate-acetone (4:1). The residue obtained by concentration of selected fractions, 0.488 g., is crystallized from acetone diluted with one-half the volume of hexane as the title compound,. white freeflowing crystals, m.p. l33.8135.0C. having R, 0.5 (T'LConsilica gel in ethyl acetate-acetone (4:1

EXAMPLE 4 p-(3-Phenylureido)phenyl Ester of PGF a (Formula Ill-F) Following the procedure of Example 1 but using 0.738 g. of PGF a, 0.347 ml. of triethylamine, 0.326 ml. of isobutylchloroformate, and 0.705 g. of phydroxy-l ,3-diphenylurea, there is obtained a crude residue. This residue is subjected to silica gel chromatography, eluting with ethyl acetate-acetone (7:3). The residue obtained by concentration of selected frac tions, 0.475 g., is crystallized from hot ethyl acetate as the title compound, white free-flowing crystals, m.p. l45.0l47.3 C., having R, 0.42 (TLC on silica gel in ethyl acetate-acetone (7:3).

EXAMPLE 5 p-Biphenyl Ester of PGF a (Formula Ill-G) Following the procedure of Example 1 but using 0.535 g. of P(iF. ,a, 0.254 ml. of triethylamine, 0.238 ml. of isobutylchloroformate, and 0.385 g. 01 p-phenylphenol, there is obtained a crude residue. This residue is subjected to silica gel chromatography, eluting with ethyl acetate followed by acetonitrile. The residue obtained by concentration of selected fractions, 0.270 g.. is crystallized from ethyl acetate diluted with an equal volume of hexane as the title compound, white l'reeflowing crystals, m.p. 1 l4.31 168 C. having R, 0.25 (TLC on silica gel in ethyl acetate).

EXAMPLE 6 p-'l'ritylphenyl Ester of P(|F. ,zx (Formula lll-H) Following the procedure of Example l but using 0.738 g. of P(il-'. .ur, 0.291 ml. of triethylamine, 0.275

ml. of isobutylchlorolormate, and 0.840 g. of p-tritylphenol, there is obtained a crude residue. 'l'his residue is subjected to silica gel chromatography, eluting with ethyl acetate water 0:1 The residue obtained by concentration of selected fractions, 0.576 g, is crystallized from acetone diluted with five volumes of hexane as the title compound, white l'recdlowing crystals, m.p. 12.18- I 29.0", having R,0.5 (TLC on silica gel in ethyl acetate).

EXAMPLE 7 p-(2 Acetamido 2-caibamoylethyl)phenyl l'ister of PUP- or (Formula Ill-l) Following the procedure ot Example 1 but using 0.738 g. of PHI-l v, 0.306 ml. of tricthylamine, 0.288 ml. of isobutvlchlorol'ormatc, and 0.488 g. ol- N acctyl [0 hexane as the title compound, white free-flowing crystals m.p. l09.8113.8 with softening at 105.0 having R, 0.5 (TLC on silica gel in ethyl acetate-methanol EXAMPLE 8 p-(2-Benzamido-2-carbamoylethyl)phenyl Ester of PGF a (Formula 111-1) Following the procedure of Example 1 but using 0.738 g. of PGF a, 0.306 ml. of triethylamine, 0.288

ml. of isobutylchloroformate, and 0.625 g. of N-benzoyl-L-tyrosinamide, there is obtained a crude residue. This residue is subjected to silica gel chromatography, eluting with ethyl acetate-tetrahydrofuran-water (:40zl). The residue obtained by concentration of selected fractions, 0.459 g., is crystallized from hot acetonitrilc as the title compound, white free-flowing crystals, m.p. 142.5l44.3 C., having R, 0.5 (TLC on silica gel in ethyl acetate-tetrahydrofuran (3:2)).

EXAMPLE 9 a-Semicarbazono-p-tolyl Ester of PGF a (Formula lll-K) Following the procedure of Example 1 but using 0.535 g. of PGF a, 0.254 ml. of triethylamine. 0.238 ml. of isobutylchloroformate, and 0.405 g. of p-hydroxybenzaldehyde semicarbazone, there is obtained a crude residue. This residue is subjected to silica gel chromatography, eluting with ethyl acetate-methanol (9:1) and ethyl acetate-methanol (8:2). The residue obtained by concentration of selected fractions, 0.215 g.. is crystallized from ethyl acetate-hexane 1:1 as the title compound, white free-flowing crystals, m.p. l 10.8l13.3 C. having R 0.4 (TLC on silica gel in ethyl acetate-methanol (9:1)).

EXAMPLE 10 p-Acetylphenyl Ester of P61 01 (Formula lll-L) Following the procedure of Example 1 but using 0.738 g. of POE- a. 0.306 ml. of triethylamine, 0.288 ml. of isobutylehlorot'ormate. and 0.299 g. of p-hydroxyacetophenone, there is obtained a crude residue. This residue is subjected to silica gel chromatography. eluting with ethyl acetate-water (99:1) followed by ethyl acetateatcetonitrile (1:1 The residue obtained by concentration of selected fractions, 0.58) g. is crystallized from ethyl acetate diluted with an equal volume of hexane as the title compound, \vhite free-flowing crystals, m.p. 85.38o.5 C. having R, 0.4 (TLC on silica gel in ethyl acetate-acetonitrilc (4:1)).

EXAMPLE ll p-Ben/oylphenyl Ester ot' P(il-. .a (Formula ill-M) Following the procedure of Example 1 but using 0.7.18 g. of P(il". .a, 0.2 1 ml. of triethylamine, 0.275 ml. of isobutylchlorot'ormate, and 0.5 4 g. ofp-hydroxybenzophenone. there is obtained a crude residue. This residue is subjected to silica gel chromatography. eluting with ethyl acetate \vater 111 l'hc residue obtained by concentration of selected fractions, 0.492 g., is crystallized'from ethyl acetate diluted with 'three volumes of hexane as the title compound, white freeflowing crystals, m.p. 73.8-75.8 C., having R, 0.5 (TLC on silica gel in ethyl acetate).

EXAMPLE 12 p-Carbamoylphenyl Ester of PGF a (Formula Ill-N) Following the procedure of Example 1 but using 0.738 g. of PGF a, 0.347 ml. of triethylamine, 0.326 ml. of isobutylchloroformate, and 0.433 g. of p-hydroxybenzamide, there is obtained a crude residue. This residue is subjected to silica gel chromatography, eluting with ethyl acetate-acetone (3:7). The residue obtained by concentration of selected fractions, 0.455 g., is crystallized from acetone diluted with an equal volume of acetonitrile as the title compound, white, freeflowing crystals, m.p. l29.5-130.8 C., having R, 0.32 (TLC on silical gel in ethyl acetate-acetone (3:7)).

EXAMPLE l3 o-Carbamoylphenyl Ester of PGF a (Formula lIl-O) Following the procedure of Example 1 but using 0.738 g. of PGF ac, 0.306 ml. of triethylamine, 0.288 ml. of isobutylchloroformate, and 0.299 g. of o-hydroxybenzamide, there is obtained a crude residue. This residue is subjected to silica gel chromatography, eluting with ethyl acetate-acetone-water (25:75:1). The residue obtained by concentration of selected fractions, 0.296 g., is crystallized from ethyl acetate diluted with 1.5 volumes of hexane as the title compound,

white free-flowing crystals, m.p. 98.5-l00.1C. having R, 0.55 (TLC on silica gel in ethyl acetate-acetone (1:3)).

EXAMPLE l4 p-(Methoxycarbonyl)phenyl Ester of PGF a (Formula III-Q) EXAMPLE Z-Naphthyl Ester of PGF a (Formula Ill-X) Following the procedure of Example 1 but using 0.535 g. of PGF oz, 0.254 ml. of triethylamine, 0.238 ml. of isobutylchloroformate, and 0.327 gfof ,B-naphthol, there is obtained a crude residue. This residue is subjected to silica gel chromatography, eluting with ethyl acetate followed by acetonitrile. The residue obtained by concentration of selected fractions, 0.410 g., is crystallized from ethyl acetate diluted with 1.5 volumes of hexane as the title compound, white free-flowing crystals, m.p. 98.8-l0OC. having R, 0.25 (TLC on silica gel in ethyl acetate).

. EXAMPLE l6 5- Sul famoyl-l-naphthyl Ester of PGF a (Formula III-Y) Following the procedure of Example 1 but using 0.738 of PGF a,"0.347 ml. of triethylamine, 0.326 ml. of isobutylchloroformate, and 0.696 g. of 1- hydroxy-S-naphthalenesulfonarnide there is obtained a crude residue. This residue is subjected to silica gel chromatography, eluting successively with ethyl acetate and ethyl acetate-acetone (1:1). The major fraction is chromatographed again, eluting with ethyl acetate-acetone (9:1 The residue obtained by concentration of selected fractions,'0.450 g., an oil, is the title compound, having R, 0.4 (TLC on silica gel in ethyl acetate).

EXAMPLE 17 9-Oxofluoren-4-yl Ester of PGF- a (Formula III-Z) Following the procedure of Example 1 but using 0.738 g. of PGF a, 0.347 ml. of triethylamine, 0.326 I EXAMPLES 18-78 The substituted phenyl and naphthyl and hydroxyfluorenone esters of PGF a, l5-methyl-PGF a, and

15(R)-15.-methyl-PGF a of Tables l-III below are obtained following the procedures of Example 1, wherein the prostaglandin compound is reacted in the presence of triethylamine and isobutylchloroformate with the appropriate hydroxy phenyl or naphthyl compound, listed in the Table. These phenols or naphthols are readily available or prepared by methods described herein or known in the art. The crude products, obtained by concentration under reduced pressure, are purified by means described herein or known in the art, including partitioning, solvent extraction, washing, silica gel chromatography, trituration, or crystallization.

Following the procedures of Examples 18-78 but employing the racemic forms of the PG compounds, there are obtained the corresponding esters of the racemic PG compounds.

TABLE I Esters of PGF a Hydroxy Phenyl or Product PGF a henzoic acid ester UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 92 9 g 2 Dated December 30, l 975 Inventr(s) wal ter Morozowich It is certified that error appears in the above-identified patent and vthat said Letters Patent are hereby corrected as shown below:

Abstract, "substituted phenyl and naphthyl and 9-oxofluoren-4-yl esters of" should read "substituted tolylesters of--. Column 2, lines 65-70, Formula H, "-C-(C H should read -C-(C H Column 3, lines -34, Formula 0, "C=C-NH should read --O=C-NH lines -36, Formula P, "-C- (CaH should read -C- (C H Column 4, l ines 8-l 0, Formula Y, "-SO NH" should read -S0 NH Column 5, lines -62, "NH-t-0 H should read --NHC-C H Column 8, line 20, "-NH 0CH should read -NH-C-8H Column l0, line 25, "-2l3.5 should read -2l8.5 Column 17, line 1 should read --where1'n E 1's--.

Signed and Scaled this A ttes t:

Rum c. MASON C. MARSHALL DANN Arresting Officer Commissioner ofPatenls and Trademarks 

1. AN OPTICALLY ACTIVE COMPOUND OF THE FORMULA
 2. The ester of N-acetyltyrosamide and PGF2 Alpha , a compound according to claim
 1. 3. The ester of N-benzoyltyrosinamide and PGF2 Alpha , a compound according to claim
 1. 4. The ester of p-hydroxybenzaldehyde semicarbazone and PGF2 Alpha , a compound according to claim
 1. 5. The ester of N-acetyl-L-tyrosinamide and 15-methyl-PGF2 Alpha , a compound according to claim
 1. 6. The ester of N-benzoyl-L-tyrosinamide and 15-methyl-PGF2 Alpha , a compound according to claim
 1. 7. The ester of p-hydroxybenzaldehyde semicarbazone and 15-methyl-PGF2 Alpha , a compound according to claim
 1. 8. Free-flowing crystals of a compound of the formula 